First animals on Earth were responsible for oxygenating the planet's oceans rather than a rise in ocean's oxygen levels causing the evolution of first animals.
Popular beliefs have it that a rise in oxygen levels of Earth's oceans led to the evolution of the first animals on the plant. A contradicting study conducted by University of Exeter says that the phenomenon may have been the other way round.
Researchers from the university suggest that the first animals on Earth were responsible for oxygenating the planet's oceans, according to a press statement. This finding challenged the preconceived notion that oxygenation of the atmosphere and oceans was a pre-requisite for the evolution of complex life forms.
"There had been enough oxygen in ocean surface waters for over 1.5 billion years before the first animals evolved, but the dark depths of the ocean remained devoid of oxygen," Professor Tim Lenton of the University of Exeter, who led the new study, said in the statement. We argue that the evolution of the first animals could have played a key role in the widespread oxygenation of the deep oceans. This in turn may have facilitated the evolution of more complex, mobile animals."
Researchers speculate that oceans were oxygenated during the Neoproterozoic Era, 1,000 to 542 million years ago. This would mean that the rise in the ocean's oxygen levels was not necessarily due to an increase in atmospheric oxygen.
Balancing oxygen supply and demand is crucial for determining the level of oxygen in the deep ocean. The demand of this gas increases when dead organic material sinks into the deep sea. Researchers of the new study found that the first animals on the planet decreased this demand by feeding on the organic materials. In turn, it increased the oxygen levels of the ocean. The oxygen-rich ocean then created ideal conditions for more mobile animals to evolve. These animals needed more oxygen to evolve, giving rise to the first predatory animals with guts that started to eat one another. The evolution of such animals marked the beginning of a modern marine biosphere.
"The effects we predict suggest that the first animals, far from being a passive response to rising atmospheric oxygen, were the active agents that oxygenated the ocean around 600 million years ago," Professor Lenton added. "They created a world in which more complex animals could evolve, including our very distant ancestors."
The new study supports the findings of another study conducted on a small sea sponge that found complex life forms on Earth don't need high levels of oxygen to grow or survive.
A previous study conducted on the origin of oxygen in the atmosphere revealed that a prior rise in oxygen level did take place but didn't lead to the evolution of complex life on the planet.
Findings of the study were published in the journal Nature Geoscience.
